The present invention relates to apparatus and methods for processing and treating various wires and cables, such as alloys of steel, for such purposes as coating with insulation; for coating metal wire and sheet materials with another metal coating; and for surface treatment of metallic wires and sheets for surface hardness. It also relates to wire and strand cable utilized in prestressed concrete structures.
In the prior art, methods for annealing and oxidizing of wire to remove known and undesirable soap or grease compounds used in drawing the wire to size is removed by heating the wire by passing an electrical current therethrough. Such a process is illustrated in U.S. Patent Ser. No. 1,993,400, issued Mar. 5, 1935, to W. H. Convers. In the foregoing patent the wire is heated continuously by passing an electrical current therethrough in an air atmosphere to annel and oxide it at atmospheric temperatures.
In U.S. Patent Ser. No. 2,300,329, issued Oct. 27, 1942, to W. H. Wood, et al, a wire in continuous operation is heated by its electrical resistance to an elevated temperature and is subsequently passed through a series of molten baths of controlled temperatures and finally quenched in an oil bath before exposure to atmosphere. In another U.S. Patent Ser. No. 2,310,451, issued Feb. 9, 1943, to W. E. Marshall, a process is disclosed for causing a phosphorus bearing surface to be formed on a sheet, strip or wire and subsequently annealed in a controlled atmosphere of reducing gas. The material is next passed through an acid solution prior to final immmersion in a galvanizing pot for final coating. In yet another U.S. Patent Ser. No. 2,794,630, issued June 4, 1957 to C. A. Turner, Jr., a strip of metal is passed continuously through a furnace heating the strip to an annealing or normalizing temperature, thence into a cooling chamber filled with a protective atmosphere which insures that the surface of the strip is bright when it leaves the chamber. While in the cooling chamber, the strip is cooled to a temperature above which it will not oxidize in the atmosphere. Oxidation of the strip occurs only between the time the strip leaves the cooling chamber and enters the quenching liquid. Thus, oxidation occurs in an air atmosphere during a relatively short distance before it enters the quenching liquid. The quenching step tends to terminate or stop the oxidizing process. The apparent purpose of the oxide coating is to enhance the tinplating or galvanizing process when the strip is used for such purposes. However, it should be noted that one of the primary purposes of the process is to stop the oxiding process rather than to encourage or increase it.
In each of the foregoing prior art and other techniques the primary purpose has been to treat the surface of the metal so that it may be utilized in an application where the metal is covered or encapsulated with another substance or material. However, the foregoing prior art nor any other known prior art has disclosed or revealed an understanding or appreciation for the difficulties to be encountered as a result of the presence of microscopic contaminants on the surface of the metal prior to the formation of the desired or required oxides or coating formed thereon. For example, it is well known that deposits of acid and other cleaning solutions residue in the smallest of cracks or pinholes on the surface of high carbon or low alloy steels, or in the crevices between strands of such steel cables may cause corrosion or contribute to hydrogen embrittlement and stress corrosion cracking of the metal which in turn tends to reduce the tensile and flexural strength of such metals. This is true when the metals are in the form of steel wire, strand cable or rope which is utilized in application of high and often continous stress conditions. The presence of other substances such as calcium stearate, sodium stearate, zinc phosphate and other phosphorous substances, as examples the formation of oxides with any of these substances present will adversely affect bond development and hence the ultimate tensile or flexural strength of cable or wire reinforced concrete structures and the like owing to their presence.
As further evidence that the prior art failed to appreciate the signifiance of surface contaminants on wire or cables and the like utilized in prestressed concrete reference is made to several prior art patents hereinbelow. In the prior art it is known to fix pretensioned wires or cables and the like into a mold after which fluent concrete is deposited onto and around such wires. Tension is placed on the wires by means of jacks, for example. After the concrete hardens the highly tensioned wires are severed at their point of entrance to the mold whereupon the stress exerted within the wires is imparted to the concrete. The individual contents of each mold are then removed and the process can be then repeated. Various processes for providing tension upon the reinforcing wires may be used in manufacturing prestressed concrete. However, there is no process known wherein advantage is taken of the coating which is formed upon the surface of treated or processed wire, strand cable, rope and the like, to thereby enhance the tensile or flexural strength of the wires utilized in such prestressed concrete structures.
More particularly, it appears that little is known about the bond development which is formed between the concrete and the wire or cable used in prestressed concrete. In fact, it is a practice in some of the prior art particularly for sleepers or railroad ties, to prevent rusting or substantially eliminate any rust from the surfaces of the wire or cable used in the manufacture of prestressed concrete structures for fear of aggressive corrosion. Such efforts clearly demonstrate a lack of understanding or appreciation for the advantages to be derived by the presence of a proper or effective rust coating on the wire or cable used for such prestressed concrete structures.
Referring to U.S. Pat. Ser. No. 3,469,829, issued Sept. 30, 1969, to Makoto Fujita et al, there is disclosed apparatus for producing wire of high tensile strength which is also capable of use in prestressed concrete. Althrough the patent recites as an object the use of the resulting processed wire for prestressed concrete, there is no disclosure of knowledge or appreciation of the need to remove microscopic contaminants which may adversely affect the bond development between the wire and concrete. As noted hereinabove, the Fujita et al patent does not disclose any recognition or appreciation for the desire or need for the presence of a rust on the wire used in the prestressed concrete structures in which their product may be employed. The Fujita patent stresses the benefits of using the high tensile strength properties of the wire produced by their process only.
Referring to another U.S. Patent Ser. No. 3,647,571, issued Mar. 7, 1972, to Kazuo Okamoto et al, there is disclosed a process for producing low relaxation or low creep characteristic steel for such uses as prestressed concrete structures. Although the patent recites the use of "air cooling", which means natural or forced air cooling, as part of a step in the process, the ultimate objective is to produce a low relaxation property for the material being processed at room and elevated temperatures. No mention or suggestion is disclosed as to the possible difficulties one might encounter by the presence of microscopic contaminants on the metal's surface which would substantially reduce bond development between the wire and cured concrete when the wires utilized are sujected to high tension therein. Here again is an excellent example of a prior art disclosure or teaching which does not recognize and/or appreciate the benefits to be derived from the use of a rust covered wire used in concrete structure. The lack of understanding or appreciation appears to arise from the fact that heretofore little was known about the chemical reaction required for enhanced bond development as disclosed and taught by the present invention.